The present invention relates to a network system for forming an L2VPN (Layer 2 Virtual Private Network) which is designed to relay layer 2 frames among a plurality of points in a user network.
A network system for forming an L2VPN based on the IEEE 802.1ah protocol (Institute of Electrical and Electronics Engineers 802.1ah, Provider Backbone Bridge (PBB)) has been proposed. In such a network system, data forwarding is executed using a MAC-in-MAC frame on a core network (also known as a backbone network) which performs as a trunk communication network. The MAC-in-MAC frame includes a MAC (Media Access Control) frame, which is a layer 2 frame, encapsulated within another MAC frame.